Chullikkattil P. Pradeep

Synthesis of Modular “Inorganic–Organic–Inorganic” Polyoxometalates and Their Assembly into Vesicles†

-capped Wells–Dawson-type clusters linkedtogether by the bis(Tris) ligands. Initial investigations intotheir thermal stability revealed that these compounds arestable up to approximately 2258C (see the SupportingInformation, Figure S1 and S2).Crystallization of1 was carried out by diffusion of diethylether into an acetonitrile solution of 1 and yellow blockcrystals were collected after one week. Single-crystal X-rayanalysis

Micropatterned surfaces with covalently grafted unsymmetrical polyoxometalate-hybrid clusters lead to selective cell adhesion.

Mn-Anderson based polyoxometalate clusters with different terminal groups have been patterned successfully onto self-assembled monolayer (SAM) using microcontact printing. Studies of the interactions between the designed SAMs and human fibroblast (hTERT-BJ1) cells have been reported, and it was observed that cells attach and spread efficiently for monolayer presenting a terminal aromatic pyrene platform with a polyoxometalate Mn-Anderson cluster as linker, demonstrating the crucial role played by the polyoxometalate metal oxide cluster as an intermediary in cell adhesion to the surface.

The Construction of High-Nuclearity Isopolyoxoniobates with Pentagonal Building Blocks: [HNb27O76]16− and [H10Nb31O93(CO3)]23−†

Big, bigger, biggest: Polyoxoniobate anions [HNb27O76]16− and [H10Nb31O92(CO3)]23−incorporate pentagonal Nb(Nb)5 building blocks; the central Nb ion is seven-coordinate within the clusters. The Nb27 species was observed using ESI-MS, thus demonstrating some solution stability; the Nb31 species is chiral and incorporates a carbonate ligand in the outer section of the cluster. The two species are the largest polyoxoniobates reported to date.

Assembly of modular asymmetric organic-inorganic polyoxometalate hybrids into anisotropic nanostructures

Three organic-inorganic hybrid Mn-Anderson polyoxometalates (POMs), with both symmetrical and asymmetrical appended groups, have been synthesized, identified using electrospray mass spectrometry, and isolated using an approach that allows the three AA, BB, and AB compounds to be structurally characterized. Investigation of the self-assembly of the hybrids on hydrophilic surfaces reveals the formation of nanofibres with characteristics that reflect the nature of the substitution of the POM yielding a route to the programmed assembly of anisotropic hybrid nanostructures.

Controllable Self-Assembly of Organic-Inorganic Amphiphiles Containing Dawson Polyoxometalate Clusters

An organic-inorganic molecular hybrid containing the Dawson polyoxometalate, ((C(4)H(9))(4)N)(5)H[P(2)V(3)W(15)O(59)(OCH(2))(3)CNHCOC(15)H(31)], was synthesized and its surfactant-like amphiphilic properties, represented by the formation of bilayer vesicles, were studied in polar solvents. The vesicle size decreases with both decreasing hybrid concentration and with increasing polarity of the solvent, independently. The self-assembly behavior of this hybrid can be controlled by introducing different counterions into the acetonitrile solutions. The addition of ZnCl(2) and NaI can cause a gradual decrease and increase of vesicular sizes, respectively. Tetraalkylammonium bromide is found to disassemble the vesicle assemblies. Moreover, the original counterions of the hybrid can be replaced with protons, resulting in pH-dependent formation of vesicles in aqueous solutions. The hybrid surfactant can further form micro-needle structures in aqueous solutions upon addition of Ca(2+) ions.

Bottom-Up Meets Top-Down Assembly in Nanoscale Polyoxometalate Clusters : Self-Assembly of [P4W52O178]24-and Disassembly to [P3W39O134]19-

The pH-controlled assembly/disassembly of a nanoscale {P4W52O178}24- cluster at pH 2 to a {P4W44O152}20- cluster at pH 3-5 via a {P3W39O134}19- cluster species at pH 2-3 to finally give {P2W19O69(OH2)}14- at pH 6 is reported. This process can be traced in the solid state crystallographically and in solution using dynamic light scattering studies.

Amphiphilic Properties of Dumbbell-Shaped Inorganic–Organic–Inorganic Molecular Hybrid Materials in Solution and at an Interface

Five novel dumbbell-shaped polyoxometalate (POM)-based inorganic-organic-inorganic molecular hybrids are investigated both in polar solvents and at interfaces for potential amphiphilic properties, which are compared with those of conventional surfactants. These hybrids with the general formula {P(2)V(3)W(15)}(2)-bis(TRIS)-linker are formed by linking two Wells-Dawson-type clusters, [P(2)V(3)W(15)O(62)](9-), with different linear bis(TRIS) linker ligands between the two TRIS moieties. Laser light scattering (LLS) studies reveal the presence of self-assembled vesicular structures in water/acetone mixed solvents, and the vesicle size increases with increasing acetone content, suggesting a charge-regulated process. The elastic constants, which are used to calculate the bending energy during vesicle formation, reveal that the organic ligands play an important role in determining the self-assembly process and that the hybrids do demonstrate amphiphilic behavior at the water/air interface. Furthermore, it is shown that some of the hybrids form monolayers at the interface, with an average molecular area that can be correlated with their organic linkers, as determined from their π-A isotherms. Finally, the hybrids not only display amphiphilic behavior akin to that of a surfactant but also exhibit an unusually high entropy contribution to vesicle formation as a result of their unique large, polar head groups, complex organic linkers, and their special molecular architectures as well as because of the involvement of the amphiphilic tetrabutylammonium (TBA) counterions.

A functional hybrid polyoxometalate framework based on a ‘trilacunary’ heteropolyanion [(P4W6O34)2Co2Na2(H2O)2]18−

Using multifunctional organocations a novel heteropolyanion, [(P4W6O34)2Co2Na2(H2O)2]18-, with unprecedented structural features, has been observed, and extension of these clusters from molecules into 1D chains occurs through a dimeric cobalt species, with this material exhibiting reversible colour/magnetic susceptibility changes upon dehydration.

Controlled assembly and solution observation of a 2.6 nm polyoxometalate ‘super’ tetrahedron cluster: [KFe12(OH)18(α-1,2,3-P2W15O56)4]29−

A nanoscale FeIII-substituted polyoxotungstate [KFe12(OH)18-(alpha-1,2,3-P2W15O56)4]29- is synthesized starting from the trilacunary {P2W15} Dawson cluster and [Fe3(mu3-O)-(CH2=CHCOO)6(H2O)3]1+ to give a 2.6 nm tetrahedral cluster species and the 16 kDa cluster can be directly observed in solution as revealed by mass spectrometry studies.

First structurally characterized optically active mononuclear Mn(IV) complex: synthesis, crystal structure and properties of [MnIVL2]{H2L = S-(−)-2-[(2-hydroxy-1-phenylethylimino)methyl]phenol}

The reaction of Mn(CH3COO)2·4H2O with H2L {H2L = S-(−)-2-[(2-hydroxy-1-phenylethylimino)methyl]phenol} in the presence of air afforded dark brown crystals of [MnIVL2], 1. Compound 1 crystallizes in the monoclinic chiral C2 space group. Crystals of 1 were further characterized by elemental analysis, room temperature magnetic moment determination, IR, UV-visible and EPR spectroscopy, cyclic voltammetry and circular dichroism (CD) studies. Cyclic voltammetry reveals a quasi-reversible redox wave corresponding to the Mn(IV)/Mn(III) couple. The EPR spectrum at liquid nitrogen temperature consists of a strong signal at g ∼ 4 and a weak but resolved response at g ∼ 2. The CD spectrum of 1 exhibits a negative band, such as shown by the enantiopure ligand H2L. Complex 1 was found to catalyze the oxidation of olefins using iodosobenzene as the oxidant in acetonitrile solutions.